Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$9.75	3.201%	$10.0621	$10.06	$10.05	$10.10
Purchase #2	$166.79	13.259%	$188.9047	$188.90	$188.90	$188.90
Purchase #3	$97.43	3.624%	$100.9609	$100.96	$100.95	$101.00
Purchase #4	$100.96	10.435%	$111.4952	$111.50	$111.50	$111.50
Purchase #5	$130.90	6.190%	$139.0027	$139.00	$139.00	$139.00
Purchase #6	$6.64	8.399%	$7.1977	$7.20	$7.20	$7.20
Purchase #7	$72.75	6.335%	$77.3587	$77.36	$77.35	$77.40
7 purchase totals =	$585.22		$634.9820	$634.98	$634.95	$635.10